1. Field of the Invention
The present invention relates to medical systems in general, and to a method and apparatus for positioning a biventricular pacemaker in the heart, in particular.
2. Discussion of the Related Art
Many people worldwide suffer from abnormal heart rhythm, where the rhythm may be too rapid, too slow, or irregular. The abnormal heart rhythm can occur in response to an emotion or event. The heart may seem to skip a beat when a person is excited, or race when a person is nervous or afraid. These sensations are called palpitations. In such cases, palpitations are usually of no consequence. However, they can be symptoms of a disorder involving abnormal heart rhythm called an arrhythmia. The regular heart beat rhythm changes its rate in response to different activities. That is, the heart speeds up or slows down to adjust the amount of blood it pumps in response to the body's needs. Heartbeats are controlled by the heart's electrical system. Electrical currents are produced and coordinated by the heart's natural pacemaker (sinus or sinoatrial node), located in the upper right heart ventricle (right chamber). The electrical currents flow through the heart along specific pathways in the heart and at a controlled speed. They stimulate the heart to contract, producing each heartbeat. Certain hormones and nerve impulses from other parts of the body signal the heart when a change in heart rate is needed. Arrhythmias are more likely to develop as people age, particularly in those who have other heart disorders. In many people, arrhythmias occur from time to time (intermittently), and some arrhythmias gradually occur more and more often and may become constant. For most people, arrhythmias are harmless, but some arrhythmias have serious consequences, such as falls, motor vehicle accidents, heart failure and occasionally, sudden death. Arrhythmias are categorized partly by their speed, into bradycardias (Slow arrhythmias) and tachycardias (fast arrhythmias). Alternatively, arrhythmias can be categorized by the causing factor. Some problems such as premature atrial beats, supraventricular tachycardia, atrial flutter, and atrial fibrillation involve the upper chambers (atriums), other problems such as premature ventricular beats, ventricular tachycardia, and ventricular fibrillation result from problems in the lower chambers (ventricles). Yet other types of arrhythmias result from problems in initiating and conducting electrical currents including malfunction of the heart block or the heart's pacemaker, such as some cases of sinus bradycardia and sick sinus syndrome.
Some arrhythmias do not require specific treatment, and many other cases can be treated effectively. Sometimes arrhythmias occur less often or even stop when patients change certain aspects of their lifestyle, such as smoking, caffeine consumption, exercise, drugs or drugs doses or the like. In yet other cases, implanting artificial pacemakers is a common treatment. Artificial pacemakers are electronic devices that act in place of the heart's own pacemaker, by sending electrical signals to the heart, and thus causing the right side of the heart to contract. An artificial pacemaker consists of a generator which is an electronics box that produces and controls the pacing signals, and is implanted surgically, usually in a pocket under the skin located below the collarbone, and connected to the heart by insulating leads or wires running inside the veins. Each wire ends with an electrode which delivers the electrical excitation generated in the pacemaker and flowing through the leads to the heart. Standard pacemakers comprise two electrodes, one is placed at the right ventricle and the other at the right atrium. Some pacemakers are on all the time, overriding the electrical impulses generated by the heart. Other pacemakers let the heart beat naturally unless it skips a beat or begins to beat at an abnormal rate. Some pacemakers, called programmable pacemakers, can be adjusted to do either. Yet another type of pacemakers has the ability to adjust their rate to the need of the patient, beating quickly during exercise and slowly during rest.
In some cases, for example when the two ventricles of the heart do not pump together which happens in approximately 20 to 30 percent of patients with heart failure, a standard pacemaker does not provide adequate treatment to the problem, and bi-ventricular pacemaker is the recommended treatment. A biventricular pacemaker stimulates both the right and left sides of the heart simultaneously. This type of pacing is also called cardiac resynchronization therapy (CRT). By stimulating both ventricles, the device makes the walls of the right and left ventricles pump together again. The heart is thus resynchronized, pumping blood more efficiently while causing less wear and tear on the heart muscle itself. Similarly to standard pacemakers, the biventricular pacemaker consists of a generator, leads and electrodes. The insulating leads are attached to the generator and carry the electrical impulses from the generator to the heart, where they are delivered by the electrodes. The leads are threaded through the veins, usually the sub-clavian vein and/or cephalic vein, which can be easily accessed from the pocket under the skin. At the tip of each lead is an electrode that delivers the necessary electrical impulses to the heart. Thus, the electric impulses are created by the generator, carried by the leads and delivered by the electrodes to the heart. The biventricular pacemaker has an additional wire (lead) over the standard pacemakers, for pacing the left ventricle in addition to pacing the right ventricle and right atrium.
As with a standard pacemaker, the first and the second wires are threaded through the veins to the right ventricle and to the right atrium. In a bi-ventricular pacemaker, a third wire is implanted into the left ventricle, in a somewhat more complicated procedure. The third wire passes through the right atrium into a vein called the coronary sinus, which drains the heart of oxygen-poor blood, and then placed through a lateral branch to pace the left ventricle. The currently employed implantation procedure consists of the following steps: bringing the third lead into the coronary vein; optionally, inside the coronary vein tree, electric excitation is applied by the electrode in multiple locations and the electric response (ECG) is measured; when a location with acceptable electric response is identified, the electrode is mounted. Navigation in the coronary venous system is performed by using fluoroscopy with injections of iodine or any other contrast agent for viewing the coronary venous system. Because of the blood flow within the venous system, from distal areas to proximal areas, the contrast material disperses too fast in the veins. Therefore, sometimes a balloon is inflated inside the coronary sinus in order to stop the blood flow. The above procedure suffers from non optimal pacemaker positioning. Since it is difficult to navigate within the venous tree, which is different from patient to patient, and specifically, the interventionist might not be able to mark and return to a previously found location which yields better ECG response. Therefore, physicians usually stop searching once an acceptable location is found, although the location might be sub-optimal.
There is therefore a need in the art for a system that will enable a physician to test the electrical response resulting from positioning the third electrode of a bi-ventricular pacemaker at multiple locations, store the response together with the corresponding locations, and be able to navigate to a location that yields the best response.